In German, it’s called “meerrettich” (sea radish) because it grows by the sea. Many believe the English mispronounced the German word “meer” and began calling it “mareradish.” Eventually it became known as horseradish. The word “horse” (as applied in “horseradish”) is believed to denote large size and coarseness.
Magellan’s expedition of 1519–1522 became the first expedition to sail from the Atlantic Ocean into the Pacific Ocean (then named “peaceful sea” by Magellan; the passage being made via the Strait of Magellan), and the first to cross the Pacific. His expedition completed the first circumnavigation of the Earth.